H.323 protocols (a proposal on packet multimedia communication system by ITU) proposed by International Telecommunications Union (ITU) are popular multimedia communication standard at present. A H.323 protocol based communication system includes two components, i.e., a gatekeeper and an endpoint. The gatekeeper is an administrator of the entire H.323 communication system, in charge of zone management, access control, address translation, broadband management, etc. The endpoint includes a node, a gateway, a Multipoint Control Unit (MCU), etc. Both an H.323 registration process and a calling process require Registration, Admission and Status signaling (RAS signaling for communication between the gatekeeper and the node specified by H.323 protocol) interaction with the gatekeeper.
In order to ensure a secure communication for the users, the H.323 communication system is provided with lots of network devices, such as gateways/firewalls, for checking network packets passing through the network devices, especially, the network packets passing through well-known ports. In practice, it often occurs that some of the signaling passing through the well-known ports is filtered, which disables the users from communicating with networks normally. To address this issue, a current solution is manual adjustment, which is to modify some of the filtering criteria configured for the firewall so that some of the signaling can pass though the well-known port. Another solution is to open a relatively convert port, i.e., an unknown port, in the firewall and then manually inform all the original users communicating with the gatekeeper via the well-known port, which means that multiple users switch to another port to communicate with the gatekeeper.
The approach of manually modifying the filtering criteria in the firewall may incur a potential security issue for the communication, whereas the approach of opening an unknown port in the firewall for subsequent communications is more applicable to a small number of users considering the fact that a registered port is open to a group of users. In the case of a large number of users, if the above described notification manner is still employed the workload of maintenance and the cost will be remarkable.
In addition, as Session Initiated Protocol (SIP), another multimedia communication standard, plays a more and more important role in multimedia communication, lots of manufacturers invest to develop products which can support both H. 323 protocol and SIP, such as node and gatekeeper. The node can not only register with an SIP proxy server, but also with a H.323 gatekeeper. In practice, some nodes need to be directed to an SIP proxy server or gatekeeper in a certain area. In this case, the direction task primarily falls on a manual switching of the protocol. In other words, supported protocols are configured at the node and it is through a manual notification to inform the node whether to register with the SIP based proxy server or to register with the H.323 based gatekeeper before the node is registered. However, when the node has registered with the SIP proxy server already, but somehow needs to switch to the H.323 gatekeeper, or when the node has registered with H.323 gatekeeper already, but somehow needs to switch to the SIP proxy server, the above described manual switching of the protocol becomes slow and inflexible.